The invention relates to a compact disconnect switch for the load circuit of a vehicle battery with the following features, that is with
an input conductor, which can be connected to an electrode terminal of the battery,
an output conductor, which can be connected to the load circuit,
a stationary contact element and a movable contact element for establishing a switching connection between the input conductor and the output conductor,
a contact carrier, which carries the movable contact element, can be switched between an opening position and a closing position and is prestressed into the opening position by spring force,
a locking mechanism, which fixes the contact carrier in the closing position or returns it into this position, and means for opening the locking mechanism.
A disconnect switch of this type is disclosed by DE 197 01 933 C1. It has a contact rocker, which is pivotably mounted in a housing and carries a movable contact indirectly via a contact spring acting as a lever arm. For returning the contact rocker into the opening position, a tear-open spring is provided. A locking mechanism comprises a setting arm and a switch pawl, the switch pawl locking the setting arm on the contact rocker and the setting arm prestressing the contact rocker in a closing position. In a way similar to the disconnect switches disclosed by DE 198 32 573 A1 or DE 197 41 919 A1, an electromagnet system with an armature which is coupled to the switch pawl is used as the means for opening the locking mechanism. For opening, the magnet system is excited, whereby the switch pawl unlocks the setting arm and the contact rocker is brought into the opening position by the tear-open spring. In the case of the known disconnect switch, however, the movable contact element located in its opening position can only be returned into the contact position manually. For this purpose, the locking mechanism must be brought back into its starting position, ensuring a closed position, for example by means of a toggle-lever joint possibly provided.
However, the use of an electromagnet system in the case of disconnect switches of this type inherently entails the risk that, in instances of severe shock impact, its armature may move even without excitation, with the result that then the load circuit is unintentionally opened. What is more, a high proportion of the weight and space requirement of the electromagnet system can be avoided. In motor vehicle construction in particular, it is indeed endeavored to keep the weight down as much as possible and, on account of the high numbers of units, also to limit the costs of small components.
The object of the present invention is to develop the disconnect switch according to the cited DE-C1 document to the extent that it is possible to dispense with a generally laborious manual resetting of the locking mechanism and that remote release is made possible. At the same time, it is intended for a compact construction of the disconnect switch to be ensured.
This object is achieved according to the invention by the means for opening the locking mechanism containing as at least one release element of a shape memory alloy, which contracts when heated by being subjected to a heating current, and by the locking mechanism having at least one spring element of a shape memory alloy which acts on the contact carrier, brings about the closing position of the latter and expands when heated by being subjected to a heating current.
The advantages associated with this configuration of the disconnect switch can be seen, inter alia, in that the use of the special release element as a means for opening the locking mechanism has the effect that it takes up much less space in comparison with an electromagnet system. Such a release element, which heats up when subjected to a heating current and thereby contracts, is generally connected to a sensor system, which is subjected to this current, for example in the event of a short-circuit or a vehicle collision. The element is heated up by the current and thus releases the opening of the locking mechanism by its contraction. Corresponding release elements are inexpensive to procure, have a low weight and are therefore also not susceptible to shock impact. Moreover, they require only little space, with the result that they can be advantageously used in a disconnect switch for the load circuit of a vehicle battery. In this case, due to the fixing of their movable contact element in the closed position by means of the locking mechanism, the contact elements are pressed so strongly against each other that even high currents, in particular as occur during the starting operation of a vehicle, can flow. With such a configuration of a disconnect switch, it can then be ensured that, in the case of use on a vehicle battery, it is possible to dispense with an electromagnet system. Consequently, the entire disconnect switch can be arranged much more easily in a housing adapted to an electrode terminal of the vehicle battery, providing a clearance for the electrode terminal itself. The space-saving makes it possible in this case for additional components to be accommodated in the housing.
Use of the special spring element likewise allows the mechanical and electrical components necessary for this purpose to be constructed in a very small space and makes remote switching possible.
Further advantageous configurations of the disconnect switch according to the invention can be taken from the dependent claims.
For instance, the locking mechanism may be formed in particular as a toggle-lever clamping mechanism. In this case, it is advantageous if the clamping element comprises a first lever, acting on the contact carrier, and a second lever, mounted in the housing, which are connected via a central toggle joint to form a toggle lever which, in the almost extended state, locks the contact carrier in its closing position.
The following configurations, to be regarded as advantageous, may also be provided in particular for the disconnect switch:
Its locking mechanism has a clamping element, which in its extended position presses the movable contact element against the stationary contact element, the release element acting on the clamping element for the opening of the locking mechanism in such a way that said clamping element buckles sideways.
The release element favorably acts via an actuating arm on the clamping element formed as a toggle lever, it being possible in a special embodiment for the actuating arm also to be formed at the same time as a return spring for the release element.
The release element acts via the actuating arm almost perpendicularly in relation to the extending axis of the toggle lever on the central toggle joint and moves the latter over the dead center when the release element contracts.
The actuating arm is formed by a cranked leaf spring, the cranked end of which presses on the toggle joint when the release element contracts.
The at least one spring element is rigidly connected on one side to the housing and acts on the opposite side on a toggle lever of the locking mechanism designed as a toggle-lever clamping mechanism. The spring element acting in this way permits a reliable and rapid return into the closing position.
The contact carrier may be a stretched-out contact spring restrained at one end in the housing, which carries the movable contact element approximately in the middle region of its length and, at its free or movable end, engages with an outer end of a first toggle joint lever, thereby forming a first pivot joint.
It goes without saying that means for manually opening and/or closing the contact elements may be additionally provided.
It is also of advantage if the release element can be activated by a short-circuit sensor and/or an acceleration sensor.
Furthermore, it may be possible for the housing to be arranged on an electrode terminal of the vehicle battery.
What is more, a current sensor which is coupled to an input conductor and applies current to the release element when a current threshold is exceeded may be provided in the housing.
An electronic evaluation circuit for activating the release element is expediently arranged in the housing. An NiTi or a NiTiCu alloy, which may possibly also include further components, is advantageously chosen as the shape memory alloy of the at least one release element and/or at least one spring element.